JP4434345B2 - Automatic focusing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic focusing apparatus and method for adjusting a focal position formed by an imaging lens, and for example, based on image information obtained by an imaging element such as a CCD solid-state imaging element, the focal position of the imaging lens is determined. The present invention relates to an automatic focusing apparatus and method for adjusting and obtaining a desired in-focus state.
[0002]
[Prior art]
In a video camera that captures the object scene and outputs the captured image, the image is captured while moving the focusing lens of the imaging lens, a high-frequency component is extracted from the output image signal, and an evaluation value for focusing is calculated. When the evaluation value increases as a result of the focusing lens movement, the movement in the same direction is continued. On the other hand, when the evaluation value decreases, the lens is moved in the reverse direction repeatedly until the evaluation value is maximized. A so-called hill-climbing servo system is used to drive the focusing lens.
[0003]
For example, Japanese Patent No. 2677036 discloses a hill-climbing autofocus system that continues a focusing operation without determining that the focal point is in focus even if a false mountain occurs in the focus evaluation value during the focusing operation in hill-climbing AF. ing. The focus control in this method is to start the focus lens in an arbitrary direction, continue to drive in the same direction if the evaluation value increases, and drive in the opposite direction if the evaluation value increases, from the increasing direction of the evaluation value to the decreasing direction. It is detected and stored that the top of the evaluation value has been passed due to a change in the value, the focusing lens is returned to the stored in-focus position, the change state of the evaluation value is monitored, and the focus is adjusted as necessary when a change occurs. This is due to the algorithm that resumes control. In this method, when there is an edge component above the threshold when the peak of the focus evaluation value appears, it is judged as a true mountain, and if there is an edge component above the threshold even if the evaluation value varies, The focusing operation is stopped unless the subject is out of focus.
[0004]
[Problems to be solved by the invention]
However, in the conventional hill-climbing servo system, the focus lens is moved while always recognizing the increase and decrease in the evaluation value, so it takes a lot of time to obtain a focusing result by hunting and the processing load is heavy. There was a problem. In addition, since this method moves the focus lens to the in-focus position, it can be effectively applied to a video camera that continuously captures a subject image and outputs it as a moving image. For example, it responds to the release switch being turned on. In a still camera that needs to be focused instantaneously in accordance with a shooting command, there is a problem that a time lag occurs until the focus lens is controlled at the in-focus position due to the extra time for this tracking. Therefore, there is a high possibility that a photo opportunity will be missed, and it cannot be applied to a still camera as it is.
[0005]
Therefore, in a still camera, in order to perform quick focusing, for example, the focusing lens is scanned so as to focus on the entire region from the infinity position to the close position, and based on image information of a plurality of frames captured during that time. An evaluation value for focusing is obtained, and shooting and recording are performed by moving the focusing lens to a position where the evaluation value is maximized. In this case, the longer the focal length of the imaging lens, the shallower the depth of field.Therefore, in order to obtain a highly accurate focusing result, it is necessary to provide many evaluation value calculation points and increase the number of focusing stages. For this reason, there is a problem that it takes much time for focusing and a heavy processing load.
[0006]
The present invention eliminates such disadvantages of the prior art, and reduces the burden on the apparatus, for example, even on the long focal length side, and provides an automatic focusing apparatus capable of obtaining a highly accurate focusing result in a shorter time. It aims to provide a method.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, the present invention provides an automatic focus adjustment apparatus that adjusts the focal position of an imaging lens that forms an image of a field of field on an imaging unit based on an imaging signal output from the imaging unit. This apparatus extracts a contrast component in a predetermined focusing area of a scene from a moving means for moving a lens for performing focus adjustment within the focus adjustment area, and an image signal output from the image sensor, and the contrast component. Evaluation value calculation means for calculating an evaluation value corresponding to each lens movement position, and a control means for controlling the movement means by obtaining the position of the lens focused on the subject in the focusing area based on the evaluation value. And a control means for counting the number of times the evaluation value continuously decreases when the lens is moved; First evaluation means for determining that the maximum value has been obtained based on the number of reductions, and the evaluation value is a predetermined value based on the maximum value of the evaluation value and the evaluation value obtained at another movement position of the lens. A second determination means for determining that there is the above, an interruption means for controlling the movement means according to the determination results of the first and second determination means, stopping the movement of the lens, and interrupting the acquisition of the evaluation value; When the process is interrupted by the means, it includes a focus determining means for moving the lens to a position where the maximum value of the evaluation value is obtained and bringing the lens into a focused state.
[0008]
In order to solve the above-described problem, the present invention provides an automatic focus adjustment method for adjusting the focus position of an imaging lens that forms an image of an object scene on the imaging unit based on an imaging signal output from the imaging unit. In this method, the moving step of moving the lens for performing the focus adjustment within the focus adjustment area, and extracting the contrast component in the predetermined focusing area of the object scene from the image signal output from the image sensor, An evaluation value calculating step for calculating an evaluation value corresponding to the contrast component for each moving position of the lens, and a control step for obtaining the position of the lens focused on the subject in the focusing area based on the evaluation value. The process includes a counting process that counts the number of times the evaluation value continuously decreases when the lens is moved, and the maximum value in the object field of the evaluation values is obtained. It is determined that the evaluation value is equal to or greater than a predetermined value based on a first determination step of determining that this is based on the number of reductions, and an evaluation value obtained at the maximum value of the evaluation value and the other movement position of the lens According to the second determination step for determining, and the determination results in the first and second determination steps, the movement of the lens is stopped, the interruption step for interrupting the acquisition of the evaluation value, and the processing is interrupted by the interruption step. And a focus determining step of moving the lens to a position where the maximum evaluation value is obtained to bring it into focus.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a digital camera to which the present invention is applied will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, a digital camera 10 having an autofocus function is shown. This camera 10 is a still camera having a movie function that continuously captures an object scene by an imaging lens 14, an aperture 16 and an imaging device (CCD) 18 provided in the imaging unit 12. A finder function at the time of imaging is provided by displaying on a liquid crystal monitor device provided in the display unit 20. When the switch S1 is turned on with the first stroke of the release button 22, the imaging lens is driven to perform focus adjustment. When the captured image is in focus and the switch S2 is turned on with the second stroke of the release button 22. The process proceeds to shooting / recording processing in the still image mode. A still image signal of one frame imaged by the imaging unit 12 is input to the recording processing unit 32 through the signal processing circuit 24, the A / D conversion circuit 26, the buffer memory 28, and the compression processing circuit 30, and is sent to a pair of 10 cameras. It is recorded on a memory card 34 that is detachably loaded.
[0010]
The image pickup lens 14 arranged in the image pickup unit 12 uses a zoom lens having a variator lens system in which the focal length is continuously variable from 7 mm on the short focus side to 21 mm on the long focus side. This is an internal focusing lens having a focusing lens system for adjusting. The imaging lens 12 may be a mechanism that adjusts the focal position by extending the entire lens or a part thereof. As shown in FIG. 4, for example, when the focal length is 7 mm, this imaging lens has a focusing lens moving distance from infinity to the closest distance, that is, the focus area is 81.7 μm, and the focusing distance when the focal length is 21 mm. Is 735 μm. The focal length and focal position of the imaging lens 14 are adjusted by the rotation of a motor or the like, and a drive signal for driving the motor is supplied from the drive circuit 36 shown in FIG.
[0011]
A diaphragm 16 for adjusting the amount of incident light is disposed in the afocal portion behind the imaging lens 14, and this diaphragm amount is adjusted by a control signal supplied from the drive circuit 36. An imaging device (CCD) 18 is disposed on the focal plane at the back of the diaphragm 16, and the imaging device 18 includes, for example, an R, G, B color filter and a microlens disposed on the imaging surface. The image pickup pixel is read out by an output amplifier as an electrical signal by a configuration including a photodiode that converts the optical image formed on the light into a charge and a charge coupled device (CCD) that transfers the charge in the vertical and horizontal scanning directions. Output. The image sensor 18 in the present embodiment has a photodiode constituting 800,000 to 1.5 million pixels, and outputs image signals of all pixels and thinned pixels in accordance with a drive signal supplied from the CCD drive circuit 38. In the moving image mode that outputs thinned pixels, the image sensor 18 transfers high-speed signal output even with a high pixel density image sensor by transferring the pixels by thinning out each half pixel in the horizontal and vertical directions, for example. To do.
[0012]
FIG. 2 conceptually shows the screen formation by the output signal of the image sensor. In the still image mode in which all pixels are read out, the screen 200 by effective pixels among the output signals of the image signal is, for example, in the horizontal direction. It is formed with 1280 pixels and 960 pixels in the vertical direction. In the moving image mode, an image signal representing the screen 202 formed with 640 × 480 pixels in the horizontal and vertical directions is output for each frame. When the power is turned on and the monitor display function is enabled, the image signal is thinned out and read out from the image sensor 18 until the second stroke of the release button 22 prior to actual shooting and recording. When the release button 22 is pressed and a first stroke is generated and the switch S1 is connected to the ground G, a plurality of frames of images corresponding to the number of focusing stages (steps) to be described later are supplied. The focusing of the imaging lens 14 is adjusted based on the signal. When the release button 22 is pressed to generate a second stroke, the switch S2 is turned on and connected to the ground G, an image signal of one frame is read out from the image sensor 18 and this still image is read. After the signal processing and compression encoding processing, the encoded data is recorded on the memory card 34.
[0013]
The output of the image sensor 18 constitutes the output of the imaging unit 12 and is connected to the signal processing circuit 24. The signal processing circuit 24 performs processing for correcting and adjusting a signal level related to brightness, color, gradation, and the like on the input image signal. Further, the signal processing circuit 24 has a function of interpolating each pixel of the RGB image signal in the still image mode, and further forming a YC format image signal composed of luminance and color components. The output of the signal processing circuit 24 is connected to an analog / digital (A / D) conversion circuit 26. The A / D conversion circuit 26 converts the image signal into, for example, 8- to 10-bit digital image data and outputs it.
[0014]
One of the outputs of the A / D conversion circuit 26 is connected to a display unit 20 having a liquid crystal panel for displaying input image data as a color image, and the other output is connected to a buffer memory 28. The buffer memory 28 is a line buffer that temporarily stores and outputs image data. In the present embodiment, image data is output at the output timing required by the evaluation value calculation circuit 42 in the moving image mode. The buffer memory 28 outputs YC image data at a timing required by the compression processing circuit 30 in the still image mode.
[0015]
The compression processing circuit 30 is an encoding circuit that compresses and encodes image data input in the still image mode in a predetermined format according to the recording medium 34 loaded in the recording processing unit 32. The compression processing circuit 30 in this embodiment performs two-dimensional DCT processing on the image data for each block of 8 × 8 pixels, and performs the Huffman coding of the processed transform coefficient, for example, by the compression coding processing such as the JPEG method, by the control unit 40. The image data is encoded at a compression rate set from The output of the compression processing circuit 30 is connected to the recording processing unit 32, and the recording processing unit 30 writes the encoded image data and its attached information to the memory card 34, and reads the information recorded on the memory card 34. It has a recording / reading function.
[0016]
When the first stroke of the release button 22 is pressed, the evaluation value acquisition circuit 42 samples G component data in the image signal input to the moving image mode under the control of the control unit 40, and within the focusing area. Is a circuit that extracts high frequency components of the image and obtains contrast information of the subject image. This contrast information is obtained by dividing the imaging range (field of view) of 480 × 640 pixels shown in FIG. 2 into a plurality of blocks 204, and a portion in one or a plurality of blocks is set as a focusing area 206, and G corresponding to the area is recorded. The evaluation value for controlling the in-focus position of the imaging lens 14 calculated based on the component image data, and the calculated evaluation value is output to the control unit 40. As the focusing area 206, a plurality of areas can be set at arbitrary positions under the control of the control unit 40. In this embodiment, four blocks in the central portion of the screen 202 are shown in FIG. It is said. The evaluation value acquisition circuit 42 has a function of determining the brightness of the entire object scene and the focusing area 206 based on the input image data, and information indicating the detected brightness is controlled by the control unit. 40, and gain control is performed for exposure control such as shutter speed and aperture value in the imaging unit 12 and signal amplification in the signal processing circuit 24.
[0017]
The control unit 40 that controls each unit detects the operation state of the release button 22 and switches between the moving image mode and the still image mode, and each unit of the camera 10 operates according to the set operation mode. For example, the CCD drive circuit 38 drives the image sensor 18 by all-pixel reading or thinning-out reading according to the set mode. Further, the control unit 40 controls the shutter speed and the aperture value in the imaging unit 12 according to the luminance information supplied from the evaluation value acquisition circuit 42. The CCD drive circuit 38 generates a drive signal that shifts the electric charge photoelectrically converted by the image sensor 18 to the vertical transfer path according to the control signal, and outputs the image signal captured at the exposure time according to the control signal. An electronic shutter control function for outputting from the image sensor is provided.
[0018]
In addition, the control unit 40 generates a processing parameter when the signal processing circuit 24 performs signal processing, and performs signal processing according to the parameter. The control unit 40 controls, for example, contour enhancement processing, color balance correction, gamma correction processing, and the like. Further, the control unit 40 has a function of setting the compression rate of the compression encoding process in the compression processing circuit 30, for example, image data at a compression rate designated by the operator according to the storage capacity of the memory card 34. Has a function of compressing and encoding. When storing the encoded image data in the memory card 34, the image processing unit 32 is supplied with information attached to the image, and the shooting date, time, exposure, etc. are stored in the area corresponding to the recording format of the memory card 34. Shooting information, compression rate and compression format information, and print information for print designation when a recorded image is printed.
[0019]
The control unit 40 also has a function of designating the focus area 206 for the evaluation value calculation circuit 42. The control unit 40 sets the focus area 206 according to the shooting situation and the operator's designation in the evaluation value acquisition circuit 42, and based on the evaluation value for automatic focus adjustment obtained in the set area 206, the imaging lens 12 Control the focal position of the. Specifically, the first stroke of the release button 22 supplies a control signal for driving an AF search that moves the focusing lens from the infinity to the closest direction in the focus area to the drive circuit 36, and an evaluation value acquisition circuit Based on the evaluation value obtained from 42, it is determined whether or not the movement is interrupted. If it is determined to be interrupted, a valid evaluation value has already been obtained, and a control signal for stopping the movement of the focusing lens is supplied to the drive circuit 36. Then, the control unit 40 moves the focusing lens backward to the place where the evaluation value indicating the maximum value is obtained, and holds the lens in that position.
[0020]
As shown in FIGS. 3 and 4, the control unit 40 sets an AF step width 302 that indicates the width of the focus lens position for calculating the evaluation value in accordance with the focus area 300 that changes in accordance with the focal length of the imaging lens 14. The number of focus steps 304 corresponding to the step width 302 is determined and determined. As shown in FIG. 3, the focus area 300 at each focal length may be equally divided by the step width 302 as shown in FIG. 3, but the step width 302 on the near distance (closest limit) side is made shorter than the infinity side. Thus, the evaluation value calculation points on the short distance side may be increased so as to increase the focus accuracy. The imaging lens 14 in the present embodiment is a zoom lens with a variable focal length. However, the imaging lens 14 is not limited to this, and is, for example, a single focus lens lined up from the short focus side to the long focus side. It may be a single focus lens that can be detachably attached to the camera body 10. In this case, the focal length and brightness (F value) of each single focus lens are transmitted to the control unit 40 of the main body 10 electrically or mechanically.
[0021]
In the drive circuit 36, in response to the control signal supplied from the control unit 40, the position of the focusing lens so that the focus position of the imaging lens 14 on the object field moves in a fixed direction from the infinity position to the closest position. Move the to perform AF search. In this embodiment, an AF search is performed to obtain an evaluation value by moving the focusing lens so that the focal point is focused from the infinity position to the closest position. However, the present invention is not limited to this, and conversely, for example, depending on the configuration of the imaging lens 14 The lens may be started to move from the closest position to the infinite position. In this case, the direction of lens movement may be switched according to whether the frequency of photographing with priority on the long-distance side or the short-distance side is high according to the photographing purpose of the photographer and the subject. For example, when macro shooting (short-distance shooting) is frequently used, if the focusing value is calculated by moving the focusing lens from the close distance side to the long distance side and the interruption is determined, the focusing lens is moved to the infinity side by interruption processing. The in-focus state can be obtained without driving. Further, when an evaluation value is obtained by moving the focusing lens so as to focus on the closest position from the infinite edge side as in this embodiment, for example, on the short distance side from 0.5 to 1.5, or about 2 meters. Since the lens position for focusing can be obtained without moving the focusing lens so as to form a focal point, it is suitable for photographing a subject at a middle distance or a long distance. As described above, since the focus limit function in the automatic focus adjustment function is provided in the present embodiment, it is possible to perform quick shooting, and the limit position is not fixed, and can be variably set according to captured image data. That is, the automatic focus adjustment is speeded up by interrupting the lens movement in an appropriate state in accordance with the photographing situation.
[0022]
The control unit 40 finally moves the focusing lens to the place where the maximum value is obtained based on the evaluation values created at the positions of the plurality of focus stages according to the focal length. Therefore, the control unit 40 has a function of recognizing the current focal length in the imaging lens 14, and determines the number of focus stages according to the focal length. The number of focus stages is supplied to the evaluation value acquisition circuit 42. The acquisition circuit 42 calculates evaluation values from image data input at a timing corresponding to the number of stages. The control unit 40 recognizes the maximum value and the minimum value of the evaluation values obtained by the acquisition circuit 42 at each focus stage.
[0023]
The control unit 40 has a function of determining how many times the evaluation value calculated at each focus stage has been continuously reduced every time the focus stage is changed. The control unit 40 counts the number of continuous decreases. When Interruption determination value C for interrupting this automatic focus adjustment (CCDAF) The In comparison, the evaluation value acquisition at each focus stage is continued until the number of consecutive decreases exceeds the interruption determination value. Conversely, when the number of consecutive decreases exceeds the interruption determination value C, the control unit 40 further calculates the difference between the maximum value and the minimum value of the evaluation values obtained so far, and further calculates the difference and a predetermined threshold value. The evaluation value is compared with K to determine whether there is an effective level difference. As a result, it is determined whether or not the subject in the focus area 206 has sufficient contrast for performing focus adjustment. Until the difference between the maximum and minimum exceeds the threshold value K, the evaluation value acquisition at each focus stage is continued. When the difference exceeds the threshold value K, the focus lens movement and evaluation value acquisition processing is interrupted. In this way, the control unit 40 detects the difference in evaluation value obtained during the movement of the focusing lens, the evaluation value continuously decreases by the number of interruption determination values, and a contrast of a predetermined level or more is detected. Then, it is determined that the maximum evaluation value has already been detected, the movement of the focusing lens is interrupted, and the evaluation value calculation is further terminated. Immediately thereafter, the control unit 40 moves the focusing lens to the position of the focusing stage where the maximum evaluation value is obtained, and maintains the focused state.
[0024]
Note that the control unit 40 in the present embodiment recognizes the minimum value of the evaluation value and calculates the difference between the maximum value and the minimum value, but is not limited to this, for example, the number of consecutive decreases is the interruption determination value. The evaluation value acquired at the lens position when this interruption determination is satisfied beyond C may be used instead of the minimum value. In other words, the control unit 40 may determine the contrast in the focus area based on the difference between the evaluation value obtained at a movement position other than the lens position where the maximum value is acquired and the maximum value.
[0025]
In the present embodiment, the control unit 40 recognizes that a mountain has already been detected when the evaluation value decreases by a predetermined number of times. Since the number of determinations (CCDAF interruption determination value) for determining the number of reductions changes according to the focal length of the imaging lens 14, the control unit 40 determines with reference to the stored table. In addition, the number of focus steps corresponding to the step width set in the focus area at each focal length is set so as to increase as the focal length changes from the short focus side to the long focus side. It is set to improve the focusing accuracy on the long focal depth side where the depth is shallow.
[0026]
Further, as shown in FIG. 4, the number of determinations (CCDAF interruption determination value C) in this embodiment is the same numerical value “4” as the number of focus steps on the short focus side or a value “4” (about 100%) close to it. It is set so that the interruption process is not substantially performed. Further, the determination number C becomes “4,4,5,6,7,8” as it approaches the long focus side, and is about 50 to 30 of the number of focusing stages “8,11,13,16,19,22”. Set to an integer value of%. This is because the focus area is short and the number of focus steps is small on the short focus side, so the focus adjustment time does not take much, and conversely, the focus area is long and the number of focus steps is large on the long focus side. This is because the focus adjustment time is required. The number C of determinations is preferably about 20 to 50% of the number of focus steps in the entire focusing area. For example, as shown in FIG. 4, when the focal length is 22 mm, the CCDAF interruption determination value is “8” with respect to the number of focus steps of 22. In this case, the number of times the evaluation value continuously decreases is 8 times. Then, it is recognized that a mountain of evaluation values has already been detected. Here, the driving of the focusing lens is stopped and the focusing lens is driven to the place where the maximum evaluation value is obtained. In this case, the position where each evaluation value is obtained may be stored in correspondence with the focus stage, and the focusing lens may be controlled at that storage position. For example, when the focal length is 22 mm, CCDAF interruption determination value "8" The position of the focusing lens may be moved backward by the same number of focus stages and returned. Further, when a plurality of values equal to the maximum value are generated, the rear pin state is prevented by setting the position corresponding to the evaluation value on the closest side to the position where the focusing lens should be moved.
[0027]
Note that when the luminance (brightness) of the object scene is low (dark) and low contrast, the control unit 40 uses a table with a CCDAF interruption determination value C larger than the value shown in FIG. If the subject has a high brightness and a high contrast, it is preferable to determine this and search for a table having a CCDAF interruption determination value C smaller than the value shown in FIG. When interruption is determined using a table configured with smaller values, the time and distance for moving the focusing lens can be further shortened.
[0028]
The control unit 40 permits photographing when the focusing lens is controlled to a position that satisfies the in-focus state, and when the second stroke is on depending on whether or not the second stroke of the release button 22 is pressed. Set the still image mode. In the still image mode, the image signal captured in the in-focus state is subjected to still image processing and compression encoded, and the encoded data is written to the memory card 34. Various types of information related to shooting and recording such as conditions and compression rate are output to the recording processing unit 32 and recorded on the memory card 34.
[0029]
The autofocus operation of the camera 10 having the above configuration will be described. When the release button 22 is pressed, the image sensor 18 is thinned out by the first stroke, and the image data of 640 × 480 pixels is sent to the evaluation value acquisition means 42. Entered. In the evaluation value acquisition means 42, an evaluation value in the focus area 206 is calculated with the partial area set by the control unit 40 in the screen represented by the image data as the focus area 206. In this embodiment, the imaging screen is divided into 64 blocks of equal area, and a plurality of blocks at locations corresponding to the imaging conditions, imaging conditions, and designation from the operator are set as the focusing area 206 for calculating the evaluation value. Next, in step 602, the current value of the focal length of the imaging lens 14 is acquired by the control unit 40, and the process proceeds to step 604 where it is confirmed that the position of the focus lens is at the infinity position. The focus lens is moved to the infinity position.
[0030]
When the initial value “0” is set in the register n of the control unit 40 in the subsequent step 606, the process proceeds to step 608 to calculate the evaluation value at the current focal position, and the calculated evaluation value is input to the control unit 40. Is done. In the control unit 40, the evaluation value at this focus stage is stored and stored, and the process proceeds to the interruption determination process shown in FIG.
[0031]
In the interruption determination process in step 700, a table value C_TABLE corresponding to the current focal length [ZOOMPOS] is set in the register C. In this case, the value 4 is set in the register C when the focal length is 7 mm to 13 mm, the value 5 is set to 13 mm and within 15 mm, the value 6 is set to 15 mm and 17 mm, and the values 7 and 19 mm are set to 17 mm and 19 mm. The value 8 is set in the register C within 21 mm.
[0032]
Next, the routine proceeds to step 702, where it is determined whether or not the evaluation value calculated by the evaluation value acquisition unit 42 has decreased continuously by the number of times set in the register C. Here, if it is determined that there is no continuous decrease, the continuation of the focus adjustment process is determined in step 704 and the process proceeds to step 612 shown in FIG.
[0033]
In step 612, it is controlled whether or not to continue the process according to the determination result in the interruption determination. In the case of continuation, the process proceeds to step 614, where it is confirmed whether the evaluation value at the last position of the focus lens, that is, the closest position has been calculated, and the evaluation value at the closest position has not yet been obtained. If so, go to Step 616. In step 616, the focus lens is moved by one AF step corresponding to the focal length at that time, and the process returns to step 608. In step 608, an evaluation value is calculated from image data of frames with different focal positions, and based on this, the processing after this step is repeated. If the evaluation value is obtained at the final position of the focusing lens in step 614, or if it is interrupted in step 612, the process proceeds to step 618.
[0034]
On the other hand, in step 702 shown in FIG. 7, when a continuous decrease in the evaluation value is detected for the number of times set in the register C, the process proceeds to step 706 and 1 is added to the value of the register n. In 708, it is determined whether or not the value of the register n exceeds the value of the register C. If the value of the register n exceeds the value of the register C, the process proceeds to step 710. Otherwise, it is determined to continue in step 704.
[0035]
Proceeding to step 710, it is determined whether the difference between the calculated maximum value (AFmax) and minimum value (AFmin) is greater than a predetermined value K. Here, if the difference between the evaluation values is larger than the value K, it indicates that there is a predetermined contrast. Therefore, the interruption of the focus adjustment is determined in step 712, and the process proceeds to step 618 shown in FIG. If the difference between the evaluation values is not greater than the value K, the process proceeds to step 704 as described above, and the continuation of the process is determined.
[0036]
When the process proceeds to the interruption process in step 612, the focusing lens is moved to the place where the maximum evaluation value is obtained in step 618, and is held at the moving position until the first stroke state is released. At the same time, the operation of the evaluation value acquisition circuit 42 is stopped, the automatic focus adjustment process is terminated, and the routine proceeds to step 620, where the photographing record permission is obtained. When the photographing / recording permission is obtained, the operation state of the release button 22 is confirmed. If the second stroke has already occurred or has occurred, the mode is shifted to the still image mode. In the still image mode, the object scene is imaged according to the current focal length and focal position, and the processed image data is compression-encoded and written to the memory card 34 together with the attached information. When this imaging process is completed, the focusing lens of the imaging lens 14 is returned to the infinity position to prepare for the subsequent shooting. If the release button 22 is continuously pressed for a predetermined time or longer after one frame is shot, it is assumed that there are new first and second strokes again, and automatic focus adjustment is resumed and repeated. .
[0037]
When these states are described according to the change state of the evaluation value shown in FIG. 5, as shown in the same figure, the evaluation value 500 initially obtained at the infinity position increases with the movement of the focusing lens. The lens moves further even after the maximum value 502 is exceeded. Then, an evaluation value 504 is obtained when the evaluation value decreases and the number of times of reduction continues six times. When the difference between the maximum evaluation value 502 and the evaluation value 500 is larger than the set value K, the processing is interrupted. Is determined. Thereafter, the focusing lens is controlled to the position of the focus stage 506 where the evaluation value 502 is obtained, and the photographing permission is lowered from the control unit 40. In this example, the evaluation value is generally ideally described, but even when the contrast difference is low, there is no peak at the center of the focus area 300 and only one side (shown in the figure). It works normally even when the right or left) is high and the other is low. In this embodiment, since the focusing lens starts to move from the infinite edge side, the effect of interruption increases as the distance is in focus. Conversely, when starting to move the focusing lens from the closest distance side, the effect of the interruption increases as the focus is in the near distance side.
[0038]
As described above, in the above embodiment, when automatic focus adjustment is performed, as the focal length of the imaging lens 14 becomes longer, the focusing lens movement is set relatively earlier in the focus area. Even if the focusing area is long and the number of focusing steps that require evaluation values for in-focus determination is large, the lens movement is interrupted when it is determined that the maximum evaluation value has already been obtained. Information necessary for focus adjustment can be obtained without scanning the entire focus area at the time of adjustment, and the focusing lens is accurately controlled to the in-focus position. As a result, focusing can be performed more quickly than before, the time lag for obtaining a still image is reduced, and the processing load related to power consumption and control associated with lens driving is reduced. For example, even if it is a short focus lens, if the number of evaluation value points is increased to increase the number of focusing steps and the focusing accuracy is increased, a short-distance shooting with a shallow depth of field and a long focus lens are used. This is especially effective when
[0039]
【The invention's effect】
As described above, according to the present invention, when obtaining an evaluation value by moving a lens for focusing, if it is determined that an effective evaluation value has been obtained and the maximum value has already been obtained, lens movement and evaluation value acquisition are performed. The process is interrupted, and it is recognized that the maximum evaluation value has already been obtained, and the lens is driven to that position. Therefore, the lens is not driven over the entire focus area, and an accurate in-focus position can be obtained. Can do. Further, by interrupting the lens movement, the processing burden and control burden are reduced, and further the power consumption is reduced. Therefore, an automatic focus adjustment device suitable for a digital camera or the like that is carried around is provided. .
[0040]
In this case, even when the focus adjustment accuracy is increased by increasing the number of focus stages as evaluation value acquisition points, the focus adjustment is performed according to the evaluation value in the focusing area obtained based on the imaging signal. In addition, since the focusing lens movement process is interrupted depending on the state of the evaluation value, the time required for focus adjustment is improved even when performing such high-performance focus adjustment. Even if it is shortened.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a digital camera to which the present invention is applied.
FIG. 2 is a diagram conceptually illustrating an imaging screen and a focusing area in a still image mode and a moving image mode.
FIG. 3 is a diagram showing a change in step width according to zooming and focusing positions.
4 is a table showing an example of a table in which values serving as a basis of the diagram shown in FIG. 3 are stored. FIG.
FIG. 5 is a graph showing an example of an evaluation value that changes as the focusing lens moves.
FIG. 6 is a flowchart showing an automatic focus adjustment operation in the embodiment.
7 is a flowchart showing details of interruption determination processing in the operation shown in FIG. 6;
[Explanation of symbols]
10 Digital camera
12 Imaging unit
14 Imaging lens
18 Image sensor (CCD)
40 Control unit (CPU)
42 Evaluation value acquisition circuit

Claims (14)

In the automatic focus adjustment device that adjusts the focal position of the imaging lens that forms an image of the object scene on the imaging unit based on the imaging signal output from the imaging unit, the device includes:
Moving means for moving a lens for performing focus adjustment within the focus adjustment area;
Evaluation value calculation means for extracting a contrast component in a predetermined focusing area of the object scene from the image signal output from the image sensor and calculating an evaluation value corresponding to the contrast component for each moving position of the lens When,
Determined based on a position of the lens for focusing with respect to the subject in the focusing region in the evaluation value, and a control means for controlling said moving means,
The control means is a counting means for counting the number of consecutive reductions in which the evaluation value continuously decreases when the lens is moved;
First determination means for determining that the maximum value in the object scene is obtained among the evaluation values based on the number of times of decrease;
Second determination means for determining that the evaluation value is equal to or greater than a predetermined value based on a maximum value of the evaluation value and an evaluation value obtained at another movement position of the lens;
Interrupting means for controlling the moving means according to the determination results of the first and second determining means, stopping the movement of the lens, and interrupting the acquisition of the evaluation value;
When the process is interrupted by the interrupting means, seen including a focusing determination unit to focus state by moving the lens by said moving means to a position where the maximum value of the evaluation value is obtained,
The control means determines whether or not to interrupt the evaluation value calculation according to the focus step value for defining the evaluation value calculation position in the focus adjustment region to which the lens is moved, and the number of times of continuous decrease. And a table for storing the interruption determination value, wherein the first determination means compares the number of consecutive reductions with the interruption determination value, and when the number of consecutive reductions exceeds the interruption determination value, An automatic focusing apparatus characterized by determining that a maximum value has been obtained . 2. The automatic focus adjustment apparatus according to claim 1 , wherein the imaging lens is a zoom lens having a variable focal length, and the focus stage value and the interruption determination value correspond to the focal length of the imaging lens in the table. Are stored,
The automatic determination apparatus according to claim 1, wherein the first determination unit determines that the maximum value is acquired based on a focus step value and an interruption determination value corresponding to a current focal length. 3. The automatic focus adjustment apparatus according to claim 2 , wherein the focus step value is set to a value that increases as the focal length increases. 3. The automatic focus adjustment apparatus according to claim 2 , wherein the interruption determination value is set so that the interruption process is performed on a long focal side of the imaging lens. The automatic focus adjustment apparatus according to claim 1 , wherein step width information for dividing the focus adjustment area of the imaging lens by a predetermined step width is stored in the table.
The automatic focus adjustment apparatus, wherein the evaluation value calculation means calculates the evaluation value based on image data captured at each position of the lens according to the step width information. 6. The automatic focus adjustment apparatus according to claim 5 , wherein the imaging lens is a zoom lens having a variable focal length, and a plurality of the step width information is stored in the table according to a focal length of the imaging lens. And the evaluation value calculation means calculates the evaluation value based on image data captured at the position of the lens according to step width information corresponding to a current focal length. apparatus.   2. The automatic focusing apparatus according to claim 1, wherein the moving means moves in one direction from one end to the other end in the focusing area, stops the lens movement by the interruption means, and An automatic focusing apparatus, wherein the lens is moved to a position where the maximum evaluation value is obtained by a focus determining means. In an automatic focus adjustment method for adjusting a focal position of an imaging lens that forms an image of an object scene on the imaging unit based on an imaging signal output from the imaging unit, the method includes:
A moving step of moving a lens for focus adjustment within the focus adjustment area;
An evaluation value calculation step of extracting a contrast component in a predetermined focusing area from the image signal output from the image sensor and calculating an evaluation value corresponding to the contrast component for each moving position of the lens When,
The position of the lens for focusing with respect to the subject in the focusing area and a control step of determining, based on the evaluation value,
The control step includes a counting step of counting the number of consecutive decreases in which the evaluation value continuously decreases when the lens is moved;
A first determination step of determining, based on the number of reductions, that the maximum value in the object scene is obtained among the evaluation values;
A second determination step of determining that the evaluation value is equal to or greater than a predetermined value based on a maximum value of the evaluation value and an evaluation value obtained at another movement position of the lens;
According to the determination results in the first and second determination steps, stop the movement of the lens and interrupt the acquisition of the evaluation value,
When the processing by the interruption process is interrupted, viewed contains a focus determination step of the maximum value by moving the lens to the resulting position is focusing state of the evaluation value,
In the first determination step, whether or not the evaluation value calculation is interrupted according to a focus step value for defining an evaluation value calculation position in a focus adjustment region to which the lens is moved and the number of continuous reductions is determined. Based on a table storing interruption determination values for determination, the number of consecutive reductions is compared with the interruption determination value, and the maximum value is obtained when the number of consecutive reductions exceeds the interruption determination value. An automatic focusing method characterized by determining that 9. The automatic focus adjustment method according to claim 8 , wherein the imaging lens is a zoom lens having a variable focal length, and the focus stage value and the interruption determination value correspond to the focal length of the imaging lens in the table. And the first determination step determines that the maximum value is acquired based on a focus step value and an interruption determination value corresponding to a current focal length. Focus adjustment method. 10. The automatic focus adjustment method according to claim 9 , wherein the focus step value is set to a value that increases as the focal length increases. 10. The automatic focus adjustment method according to claim 9 , wherein the interruption determination value is set so that the interruption process is performed on a long focal side of the imaging lens. 9. The automatic focus adjustment method according to claim 8 , wherein the table stores step width information for dividing the focus adjustment area of the imaging lens by a predetermined step width, and the evaluation value calculation step includes the step width. An automatic focus adjustment method characterized in that the evaluation value is calculated based on image data captured at each position of the lens according to information. An automatic focusing method according to claim 12, before Symbol table, the step width information are more stored according to the focal length of the imaging lens, the evaluation value calculating step, the current focal length An automatic focus adjustment method, wherein the evaluation value is calculated based on image data picked up at a position of the lens corresponding to the corresponding step width information. 9. The automatic focus adjustment method according to claim 8 , wherein the moving step moves in one direction from one end to the other end in the focus adjustment region, stops the lens movement in the interruption step, and An automatic focus adjustment method, wherein the lens is moved to a position where the maximum evaluation value is obtained by a focus determination step.

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